Analyses of Precipitation and Evapotranspiration Changes Across the Lake Kyoga Basin in East Africa
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water Article Analyses of Precipitation and Evapotranspiration Changes across the Lake Kyoga Basin in East Africa Charles Onyutha * , Grace Acayo and Jacob Nyende Department of Civil and Building Engineering, Kyambogo University, P.O. Box 1, Kyambogo, Kampala, Uganda; [email protected] (G.A.); [email protected] (J.N.) * Correspondence: [email protected] Received: 15 March 2020; Accepted: 15 April 2020; Published: 16 April 2020 Abstract: This study analyzed changes in CenTrends gridded precipitation (1961–2015) and Potential Evapotranspiration (PET; 1961–2008) across the Lake Kyoga Basin (LKB). PET was computed from gridded temperature of the Princeton Global Forcings. Correlation between precipitation or PET and climate indices was analyzed. PET in the Eastern LKB exhibited an increase (p > 0.05). March–April–May precipitation decreased (p > 0.05) in most parts of the LKB. However, September–October–November (SON) precipitation generally exhibited a positive trend. Rates of increase in the SON precipitation were higher in the Eastern part where Mt. Elgon is located than at other locations. Record shows that Bududa district at the foot of Mt. Elgon experienced a total of 8, 5, and 6 landslides over the periods 1818–1959, 1960–2009, and 2010–2019, respectively. It is highly probable that these landslides have recently become more frequent than in the past due to the increasing precipitation. The largest amounts of variance in annual precipitation (38.9%) and PET (41.2%) were found to be explained by the Indian Ocean Dipole. These were followed by precipitation (17.9%) and PET (21.9%) variance explained by the Atlantic multidecadal oscillation, and North Atlantic oscillation, respectively. These findings are vital for predictive adaptation to the impacts of climate variability on water resources. Keywords: precipitation variability; potential evapotranspiration; climate indices; trend analyses; climate variability; Lake Kyoga Basin; Bududa landslides; Hargreaves method 1. Introduction Within the River Nile basin, Lake Kyoga links Lake Victoria to Lake Albert. However, the Lake Kyoga Basin (LKB) is the least studied among the River Nile tributaries [1]. This is due to lack of quality observed long-term hydrometeorological data. Generally, in the sub-Saharan Africa (where the LKB is located), weather stations are of low density, unevenly distributed, and not continuously operational due to poor maintenance of data recording equipment or instruments [2]. In some cases, studies tend to be conducted using short-term data. For instance, to investigate the groundwater–surface water interactions of papyrus wetlands in the LKB, Southwell [3] used data observed from July 2015 to February 2016. Such short-term data cannot be representative of the long-term variation in the hydrometeorology. Generally, to circumvent the problem of lack of historical long-term series, studies tend to make use of the reanalyses or remotely sensed datasets. A few examples of precipitation products and/or temperature datasets freely available to researchers can be obtained from the Princeton Global Forcings (PGFs) [4], Global Precipitation Climatology Project (GPCP) [5], Climatic Research Unit (CRU) [6], African Rainfall Climatology (ARC) [7], Tropical Rainfall Measuring Mission (TRMM) [8], and Climate Forecast System Reanalysis (CFSR) of the National Centers for Environmental Prediction (NCEP) [9]. The temperature from some of the freely downloadable datasets can be used to estimate Potential Water 2020, 12, 1134; doi:10.3390/w12041134 www.mdpi.com/journal/water Water 2020, 12, 1134 2 of 23 Evapotranspiration (PET). Several studies (for instance, [10–13]) that made use of the freely available precipitation products. The main advantage of reanalyses data is that they tend to be of a large (or global) spatial scale. In hydrology, hydrometeorology, and perhaps other fields, precipitation and evapotranspiration are respectively the first and second largest terms in relation to the water budget. Especially for the estimation of PET, several studies [14–19] made use of remotely sensed and/or satellite images. Glenn et al. [14] in their review put emphasis on studies that combine methods for estimating evapotranspiration from remote sensing and ground observations considering areas such as agricultural region, rangelands, and natural ecosystems. Vinukollu et al. [15] compared the performance of a single source energy budget model, Penman–Monteith approach, and Priestley–Taylor method for estimating evapotranspiration at a global scale. Where soil evaporation plays a dominant role, the Priestley–Taylor approach and the single source energy budget model yielded results, which were highly comparable with ground-based observations of evapotranspiration; however, the Penman–Monteith method showed the highest correlation for sensible heat flux [15]. Bashir et al. [19] assessed the applicability of evapotranspiration estimates from remotely sensed data for managing of Gezira Scheme in Sudan. Alemu et al. [17] investigated the association between evapotranspiration and vegetation dynamics in the River Nile basin. Liou and Kar [18] conducted a review of evapotranspiration estimation with remote sensing and a number of surface energy balance algorithms. For the study area, Nsubuga et al. [20] used remotely sensed Landsat images for 1986, 1995, and 2010 to detect changes in the surface water area of the LKB. Nsubuga et al. [20] showed that the surface area of Lake Kyoga was increasing. Such findings are relevant for applications, which directly depend on the Lake Kyoga and its outflow. The main challenge with remotely sensed data or satellite images is that they tend to be of short term. Furthermore, acquiring an archive of such imagery with high spatial and temporal resolution is always very expensive. Therefore, given that in the analyses of trends and variability, long-term data are required, reanalyses data can be used based on the intended applications or the purpose for which the study is being conducted. There are a number of water resources applications within the LKB. Some of these applications include the 600 Mw Karuma hydro power plant (located shortly downstream of the Lake Kyoga outflow), as well as the several irrigation schemes such as Agoro, Doho, and Olwenyi in Lamwo, Butaleja, and Lira Districts, respectively. In Bududa district, which is located in the Eastern part of the LKB, the occurrence of precipitation-induced landslides is common. The recent landslide occurred in December 2019 [21]. Therefore, for an insight on the variation in the water budget of the LKB, it is important to assess precipitation and PET changes in terms of long-term trends, and/or multidecadal variability. Whereas long-term trends may be due to global warming, precipitation and PET decadal or multidecadal variability can be to a number of drivers. Such drivers can include the changes in large-scale ocean–atmosphere conditions, as well as the influence from regional and local factors. Dry and wet conditions across the East Africa where the LKB is located can be linked to the increase or decrease in the Sea Surface Temperature (SST) or atmospheric pressure at the sea level across the various oceans. When precipitation or PET variability drivers are known, an upcoming period of wet or dry condition can be predicted thereby supporting planning of predictive adaptations to the impact of climate variability on water resources, and agriculture. This study aimed at analyzing precipitation and PET trends and variability across the LKB. This, while focusing on the rainy season as well as annual time scale, was done while investigating the possible linkage of the precipitation and PET variability to the changes in large-scale ocean–atmosphere conditions. Water 2020, 12, 1134 3 of 23 2. Materials and Methods 2.1. The Study Area The LKB is found in the upper part of the River Nile Basin. It is located in Uganda, a country found in East Africa. Apart from Lake Kyoga, the LKB comprises Lake Bisina and Lake Nakuwa with the open water surface areas of 130 km2 and 83 km2, respectively [22]. The Lake Kyoga receives flows from the Victoria Nile and the tributaries emanating from the Mount Elgon region. The Lake Kyoga is shallow (with most parts less than 4 m deep) but connects Lake Victoria to Lake Albert. The drainage area of the LKB has been reported differently by many researchers as 75,000 km2 [23], 57,233 km2 (Food and Agriculture Organization FAO [24]), and about 57,000 km2 [1,25]. Nevertheless, the drainage area of the LKB stretches between 0◦ N and 4◦ N (in the North–South direction) and 32◦ E and 35◦ E (in the East–West direction). The vast drainage area of the LKB is exclusively within the confines of the territorial boundary of Uganda. The study area starts from the central part of the country and extends through the eastern region until the northeastern subregion. The LKB consists of eleven subcatchments including Awoja, Okok, Okere, Mpologoma, Victoria Nile, Sezibwa, Akweng, Abalang, Lwere, Lumbuye, and Kyoga Lake side zones (Figure1). There are a number of ethnic tribes found within the LKB including (among others) the Buganda, Busoga, Iteso, Kumam, Jopadhola, Sebei, Lango, and Karamojong. The main occupation of the people in the LKB is subsistence farming. Fishing is another key occupation especially for those close to the shoreline of the Lake Kyoga. However, in the far northeastern part of the LKB, the Karamojongs are nomadic pastoralists and tend to move from place to place in search for pasture and water for their livestock. In Figure1, the background map of the LKB is the Digital Elevation Model (DEM). The hole-filled DEM derived from the USGS/NASA [26] and processed by the International Centre for Tropical Agriculture (CIAT-CSI-SRTM) using interpolation methods described by Reuter et al. [27] was downloaded online via the link http://srtm.csi.cgiar.org (accessed: 3 December 2019). It is noticeable that the elevation ranges from about 1000 to 4320 m above sea level. The highest point (4320 m) is the peak of Mount Elgon located in the Eastern part of the LKB.